Electronic camera and method with fill flash function

ABSTRACT

A method and camera for electronic image capture provide an electronic image capture device, a scanning aperture shutter located to control light energy received by the image capture device, a flash unit oriented to illuminate an image scene, a photocell unit adapted for sensing visible spectrum energy and infrared spectrum energy received from the image scene, and an exposure control system responsive to the photocell unit and operatively connected to the scanning aperture shutter and the flash unit. The exposure control system is adapted to control an amount of fill flash energy received from the image scene in relation to visible ambient light energy received from the image scene during image capture by illuminating the flash unit once a predetermined amount of ambient visible spectrum energy is sensed by the photocell unit and by extinguishing the flash unit once a predetermined amount of infrared energy is sensed by the photocell unit.

FIELD OF THE INVENTION

The present invention generally relates to electronic image capture andparticularly to a fill flash function for such electronic image capture.

BACKGROUND OF THE INVENTION

Electronic imaging devices, such as those used in digital cameras,typically perform image capture differently from film based cameras.Electronic image capture devices typically integrate separate outputsignals from each photosensitive semiconductor pixel of an array ofpixels. An image capture is typically initiated by simultaneouslyzeroing all of the integration values of the pixels, and variousapproaches have been used for terminating the image capture process.Such integrated values then need to be read out from each of the arraypixels. Problems occur in controlling the amount of time over which eachof the pixels continues to integrate sensed light signals.

Controlling the integration of such imaging devices is furthercomplicated by the attempt to control a fill flash function, wherein aflash unit is used for part of the illumination of a scene including anear field object of limited brightness and a far field background ofgreater brightness. Such image capture and pixel integration is stillfurther complicated by the additional need to achieve the proper balanceof illumination between natural and artificial, or flash, light sources.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an electronic camera,including an electronic image capture device adapted for capturing animage scene, a scanning aperture shutter located to control light energyreceived by the electronic image capture device from the image scene, aphotocell adapted for sensing light energy received from the imagescene, and an exposure control system responsive to the photocell andoperatively connected to the scanning aperture shutter, wherein theexposure control system is adapted to control the scanning apertureshutter and a flash unit in response to sensed light energy at thephotocell to control an amount of fill flash energy in relation toambient light energy received by the electronic image capture systemduring image capture.

The exposure control system may be adapted to illuminate the flash unitonce a predetermined amount of ambient light energy is sensed by thephotocell, and also to extinguish the flash unit once a predeterminedamount of infrared spectrum energy is sensed by the photocell duringflash unit illumination.

The photocell may include a visible spectrum photocell and an infraredspectrum photocell, and the exposure control system may adapted to usethe visible spectrum photocell to sense ambient light energy receivedfrom the image scene prior to illumination by the flash unit and to usethe infrared photocell for sensing infrared spectrum energy receivedfrom the image scene during illumination by the flash unit. Also, thescanning aperture shutter may include separate apertures for the imagecapture device, the visible spectrum photocell and the infrared spectrumphotocell.

The exposure control system may be adapted to generate control signalsfor a detachable flash unit, or the flash unit may be constructedintegrally with the camera.

Another embodiment of the present invention includes an electronic imagecapture device adapted for capturing an image scene, a scanning apertureshutter located to control light energy received by the image capturedevice, a flash unit oriented to illuminate the image scene, a photocellunit adapted for sensing visible spectrum energy and infrared spectrumenergy received from the image scene, and an exposure control systemresponsive to the photocell unit and operatively connected to thescanning aperture shutter and the flash unit, wherein the exposurecontrol system is adapted to control an amount of fill flash energyreceived from the image scene in relation to visible ambient lightenergy received from the image scene during image capture byilluminating the flash unit once a predetermined amount of ambientvisible spectrum energy is sensed by the photocell unit and byextinguishing the flash unit once a predetermined amount of infraredenergy is sensed by the photocell unit.

The visible spectrum and infrared spectrum photocells may be separatedevices, and the shutter may include separate, proportionately operable,variable apertures for the image capture device and the photocell unit.Also, the flash unit may be a quenchable strobe light.

Yet another embodiment of the present invention provides a method forelectronic image capture using a fill flash function, comprising thesteps of using a scanning aperture shutter to control light energyreceived by an electronic image capture device, sensing visible ambientlight energy and infrared energy received from an image scene, andcontrolling the scanning aperture shutter and a flash unit during imagecapture in response to the sensing to cause a predetermined ratio offill flash light energy to ambient light energy to be received by theelectronic image capture device including illuminating the flash unitonce a predetermined amount of ambient light energy is sensed duringimage capture.

The step of sensing may use an infrared spectrum photocell for sensinginfrared energy received from the image scene during illumination by theflash unit, and further may use a visible light spectrum photocell forsensing ambient light energy received from the image scene beforeillumination by the flash unit.

The step of controlling may include extinguishing the flash unit once apredetermined amount of infrared spectrum energy is sensed during flashunit illumination. Also, scanning aperture shutter may include separate,proportionately operable, variable apertures for image capture and thestep of sensing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustratively shown and described in referenceto the accompanying drawings, in which:

FIG. 1 is a representational side view diagram of an electronic cameraconstructed in accordance with one embodiment of the present inventionas it would be used for image capture;

FIG. 2 is a representational front view of a blade shutter suitable foruse with the camera of FIG. 1;

FIG. 3 is a representational front view of another blade shuttersuitable for use with the camera of FIG. 1; and

FIG. 4 is a graph of light energy captured by the camera of FIG. 1,verses time.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an electronic camera 10 generally including an electronicimage capture device 12, a scanning aperture shutter 14, imaging optics16, a photocell 18 and an exposure control system 20. Attached to camera10 is a removable flash unit 22. Camera 10 forms an electronic imagecapture system by using imaging optics 16, such as a lens, to focus animage scene of received light from a field of view 24, on image capturedevice 12. Scanning aperture shutter 14 is located between imagingoptics 16 and image capture device 12 to control the amount of imagelight received by image capture device 12.

Photocell 18 is directed to sense light energy received from asubstantially similar field of view 26, as determined by a separateoptical element 28. Light energy received by photocell 18 passesthrough, and is likewise controlled by shutter 14. In this manner, thelight energy sensed by photocell 18 is analogous to the light energyreceived by image capture device 12.

Exposure control system 20 is coupled to photocell 18 and is adapted toresponsively control shutter 14 and image capture device 12 to controlthe amount of light energy received from flash unit 22 during imagecapture.

Image capture device 12 may be constructed in any suitable manner, suchas in the form of a CCD, which is the best available embodiment at thetime of this application. Also, although flash unit 22 is shown as aremovable attachment to camera 10, it may also be constructed as anintegral part of camera 10, as represented by phantom lines 23.

As is frequently the case, an image scene 30 may include a near-fieldobject 32 set against a far-field background 34, wherein the naturalillumination of far-field background 34 is greater than that ofnear-field object 32. In this case, a fill flash function is used toprovide greater illumination to the near-field object 32 and therebybalance the lighting of the entire photo for better composition. Fillflash is even more frequently used to minimize shadow areas in nearfield objects. For these purposes, exposure control system 20 is adaptedto control the amount of fill flash energy received from flash unit 22in relation to ambient light energy received during an image capture.

FIG. 2 is a representational front view of one form of scanning apertureshutter 14, called a blade shutter, which may be used with the camera 10(FIG. 1). Shutter 14 typically includes a pair of rigid shutter blades40, 42, which are adapted for relative lateral movement in the directionof arrows 44 by means of an electromechanical actuator 45. Front bladeshutter 40 includes apertures 46, 48, and rear blade shutter 42 includesapertures 47, 49, shown in phantom. Aperture pair 46, 47 are intendedfor image capture and are aligned with image capture device 12 (FIG. 1).Aperture pair 48, 49 are intended for exposing photocell 18 (FIG. 1) toincident image light energy and are therefore intended to be alignedwith photocell 18.

The relative lateral movement of shutter blades 40, 42 causes aperturepairs 46, 47 and 48, 49 to progressively overlap and thereby increasethe aperture size for incident light energy. The separate aperture pairs46, 47 and 48, 49 are proportionately sized so that any relativepositioning of shutter blades 40, 42 results in generally the sameproportion of light energy emitted through aperture pairs 46, 47 and 48,49. Thus, the amount of light energy sensed by photocell 18 generallyrepresents the same proportion of the light energy emitted throughaperture pair 46, 47, regardless of the position of shutter blades 40,42. In this manner, shutter 14 includes separate, proportionatelyoperable, variable apertures 46, 47 and 48, 49 for image capture device12 and photocell 18. The art of constructing blade shutters is welldeveloped and many variations from the art may be used with the presentinvention. Although lateral movement of shutter blades 40, 42 isdescribed, alternative forms of movement, such as rotational, may beused. Likewise, relative shapes and sizes may be varied in accordancewith known methods. Although FIG. 2, depicts a single photocellaperture, more than one may be used, and their orientation may vary.

FIG. 3 shows a front view of another pair of blade shutters 50, 52,which include an aperture pair 54, 55 for image capture and separateaperture pairs 56, 57 and 58, 59 to accommodate a visible spectrumphotocell 60 and an infrared spectrum photocell 62, respectively.Aperture pair 56, 57 are associated with a monitoring aperture pair 64,which is shown as a single aperture, but is actually a separate aperturein each aperture blade 50, 52. Monitoring aperture pair 64 is designedto be open while aperture pair 54, 55 is closed to allow ambient lightmonitoring of an image scene prior to image capture. Both aperture pairs56, 57 and 58, 59 are shaped to provide an analogous representation ofthe opening of image capture aperture pair 54, 55. The relativeorientation of the aperture pairs varies between FIGS. 2 and 3 as theorientation of image capture device 12 and photocell 18 may vary in theembodiment of FIG. 1.

Thus any suitable arrangement of apertures may be used, depending uponthe specific photocell arrangement employed. Photocell 18 may take anysuitable form such as separate visible spectrum and infrared spectrumphotocells, or a single unit adapted to separately sense visible andinfrared spectrum energy.

FIG. 4 is a graph, over the exposure time of an image capture, of theamount of light energy admitted through image capture aperture pair 46,47 (FIG. 2) to thereby form an image on image capture device 12 (FIG.1). FIG. 4 represents the operation of camera 10 (FIG. 1) in the fillflash mode, wherein the total light energy used for image capture is amixed proportion of ambient scene illumination and fill flash. Asmentioned, photocell 18 senses an analogous amount of received lightduring image capture. Whereas the instantaneous value of curve 68represents the light level being received, the area 70, 72 under thegraph represents the amount of light energy received over time. In thismanner, by monitoring and integrating the output of photocell 18,exposure control system 20 can determine, in real time, the amount ofimage capture light energy incident upon image capture device 12.

A well known fill flash function typically uses ambient sceneillumination to provide approximately 75% of the image capture lightenergy and the fill flash function to provide the remaining 25% of imagecapture energy. This distribution may be varied by image scene. Forcontrolling this distribution, exposure control system 20 monitors andintegrates the output of photocell 18 until the integrated area 70 undercurve 68 reaches approximately 70% of the necessary amount of imagecapture light energy. At this point 74, flash unit 22 is illuminated andthe amount of incident light energy sensed by photocell 18 increases,very steeply. At some point 76, exposure control system 20 determinesthat 90 to 95% of the desired image capture light energy has beenreceived and exposure control system 20 quenches flash 22 and closesshutter 14. In a this manner, flash unit 22 may have a variable lightoutput, and exposure control system 20 may be adapted to limit suchvariable light output in response to light energy sensed by photocell18.

The rising slope of the left side of curve 68 represents the increasingaperture size of a scanning aperture shutter. It can be appreciated,that in low-light image scenes, the scanning aperture shutter may opento its maximum aperture before approximately 70% of the image captureenergy has been sensed or received. In this situation, exposure controlsystem 20 may be programmed to illuminate flash unit 22 to allow the 25%flash contribution to be collected. Shutter 14 may subsequently be leftopen after flash unit 22 is quenched, so that ambient light is furtheradmitted to reach the preferred distribution. Ambient light receivedduring flash illumination may not be measurable because of visiblespectrum flash illumination, but it may be factored into themeasurement.

It is known in flash unit technology that the amount of infrared flashenergy reflected by objects is more consistent between various objectsthan the amount of visible spectrum energy. For this reason, the presentinvention preferably uses an infrared photocell for measuring imagescene energy during flash illumination, and those measurements areconverted to appropriate visible spectrum values or otherwise factoredinto the overall light measurement in accordance with methods known inthe art. The art of exposure control devices for cameras is welldeveloped, and various physically different devices may be constructedin accordance with known methods to implement the functions of theexposure control system of the present invention.

The present invention is illustratively described above in reference tothe disclosed embodiments. Various modifications and changes may be madeto the disclosed embodiments by persons skilled in the art withoutdeparting from the scope of the present invention as defined in theappended claims.

1. An electronic camera, comprising: an electronic image capture deviceadapted for capturing an image scene; a scanning aperture shutterlocated to control light energy received by said electronic imagecapture device from said image scene; a photocell adapted for sensinglight energy received from said image scene; and an exposure controlsystem responsive to said photocell and operatively connected to saidscanning aperture shutter, wherein said exposure control system isadapted to control said scanning aperture shutter and a flash unit inresponse to sensed light energy at said photocell to control an amountof fill flash energy received by said electronic image capture system inrelation to ambient light energy received by said electronic imagecapture system during image capture.
 2. The camera of claim 1, whereinsaid exposure control system is adapted to illuminate said flash unitonce a predetermined amount of ambient light energy is sensed by saidphotocell.
 3. The camera of claim 2, wherein said exposure controlsystem is adapted to extinguish said flash unit once a predeterminedamount of infrared spectrum energy is sensed by said photocell duringflash unit illumination.
 4. The camera of claim 1, wherein saidphotocell includes a visible spectrum photocell and an infrared spectrumphotocell, and further wherein, said exposure control system is adaptedto use said visible spectrum photocell to sense ambient light energyreceived from said image scene prior to illumination by said flash unitand to use said infrared photocell for sensing infrared spectrum energyreceived from said image scene during illumination by said flash unit.5. The camera of claim 4, wherein said scanning aperture shutterincludes separate apertures for said image capture device, said visiblespectrum photocell and said infrared spectrum photocell.
 6. The cameraof claim 1, wherein said exposure control system is adapted to generatecontrol signals for a detachable flash unit.
 7. The camera of claim 1,wherein said flash unit is constructed integrally with said camera. 8.An electronic camera, comprising: an electronic image capture deviceadapted for capturing an image scene; a scanning aperture shutterlocated to control light energy received by said image capture device; aflash unit oriented to illuminate said image scene; a photocell unitadapted for sensing visible spectrum energy and infrared spectrum energyreceived from said image scene; and an exposure control systemresponsive to said photocell unit and operatively connected to saidscanning aperture shutter and said flash unit, wherein said exposurecontrol system is adapted to control an amount of fill flash energyreceived from said image scene in relation to visible ambient lightenergy received from said image scene during image capture byilluminating said flash unit once a predetermined amount of ambientvisible spectrum energy is sensed by said photocell unit and byextinguishing said flash unit once a predetermined amount of infraredenergy is sensed by said photocell unit.
 9. The camera of claim 8,wherein said visible spectrum and infrared spectrum photocells areseparate devices.
 10. The camera of claim 9, wherein said shutterincludes separate, proportionately operable, variable apertures for saidimage capture device and said photocell unit.
 11. The camera of claim11, wherein said flash unit is a quenchable strobe light.
 12. A methodfor electronic image capture using a fill flash function, comprising thesteps of: using a scanning aperture shutter to control light energyreceived by an electronic image capture device; sensing visible ambientlight energy and infrared energy received from an image scene; andcontrolling said scanning aperture shutter and a flash unit during imagecapture in response to said sensing to cause a predetermined ratio offill flash light energy to ambient light energy to be received by saidelectronic image capture device including illuminating said flash unitonce a predetermined amount of ambient light energy is sensed duringimage capture.
 13. The method of claim 12, wherein said step of sensinguses an infrared spectrum photocell for sensing infrared energy receivedfrom said image scene during illumination by said flash unit.
 14. Themethod of claim 13, wherein said step of sensing uses a visible lightspectrum photocell for sensing ambient light energy received from saidimage scene before illumination by said flash unit.
 15. The method ofclaim 12, wherein said scanning aperture shutter includes separate,proportionately operable, variable apertures for image capture and saidstep of sensing.
 16. The method of claim 12, wherein said step ofcontrolling includes extinguishing said flash unit once a predeterminedamount of infrared spectrum energy is sensed during flash unitillumination.